<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>

<body>
    <input type="text" placeholder="mao" class="sky">
</body>
<script src="../jquery.min.js"></script>
<script>
    $(".sky").val("moon")
    console.log($(".sky").val()); //
</script>

</html>